Cancer, the uncontrolled growth of malignant cells, is a major health problem of the modern medical era and is one of the leading causes of death in developed countries. In the United States, one in four deaths is caused by cancer (Jemal, A. et al., CA Cancer J. Clin. 52:23-47 (2002)). Among cancers, those that arise from organs and solid tissues, known as solid cancers (e.g., colon cancer, lung cancer, breast cancer, stomach cancer, prostate cancer, pancreatic cancer) are among the most-commonly identified human cancers.
For example, prostate cancer is the most frequently diagnosed noncutaneous malignancy among men in industrialized countries, and, in the United States, 1 in 8 men will develop prostate cancer during his life (Simard, J. et al., Endocrinology 143(6):2029-40 (2002)). The incidence of prostate cancer has dramatically increased over the last decades and prostate cancer is now a leading cause of death in the United States and Western Europe (Peschel, R. E. and J. W. Colberg, Lancet 4:233-41 (2003); Nelson, W. G. et al., N. Engl. J. Med. 349(4):366-81 (2003)). An average 40% reduction in life expectancy affects males with prostate cancer. If detected early, prior to metastasis and local spread beyond the capsule, prostate cancer can often times be cured (e.g., using surgery). However, if diagnosed after spread and metastasis from the prostate, prostate cancer is typically a fatal disease with low cure rates. While prostate-specific antigen (PSA)-based screening has aided early diagnosis of prostate cancer, it is neither highly sensitive nor specific (Punglia et al., N. Engl. J. Med. 349(4):335-42 (2003)). This means that a high percentage of false negative and false positive diagnoses are associated with the test. The consequences are both many instances of missed cancers and unnecessary follow-up biopsies for those without cancer.
Breast cancer remains the second leading cause of cancer-related deaths in women, affecting more than 180,000 women in the United States each year. For women in North America, the life-time odds of getting breast cancer are now one in eight. Although the discovery of BRCA1 and BRCA2 were important steps in identifying key genetic factors involved in breast cancer, it has become clear that mutations in BRCA1 and BRCA2 account for only a fraction of inherited susceptibility to breast cancer (Nathanson, K. L., et al., Human Mol. Gen. 10(7):715-720 (2001); Anglican Breast Cancer Study Group. Br. J. Cancer 83(10):1301-08 (2000); and Syrjakoski, K., et al., J. Natl. Cancer Inst. 92:1529-31 (2000)). Despite considerable research into therapies for breast cancer, breast cancer remains difficult to diagnose and treat effectively, and the high mortality observed in breast cancer patients indicates that improvements are needed in the diagnosis, treatment and prevention of the disease.
Excluding skin cancer, colorectal cancer is the third most frequently diagnosed cancer in the United States and Canada (after lung and breast in women, and lung and prostate in men). The American Cancer Society estimates that there will be approximately 145,000 new cases of colorectal cancer diagnosed in the U.S. in 2005. Colorectal cancer is the second leading cause of cancer death among men and women in the United States and Canada (after lung cancer).
The annual incidence of pancreatic cancer is nearly equivalent to the annual mortality, estimated to be 31,860 and 31,270, respectively, in the U.S. in 2004. Patients with locally advanced and metastatic pancreatic cancer have poor prognosis, and diagnosis generally occurs too late for surgery or radiotherapy to be curative (Burr, H. A., et al., The Oncologist 10(3): 183-190, (2005)). Chemotherapy can provide relief of symptoms for some patients with advanced pancreatic cancer, but its impact on survival has been modest to date.
In the United States, more than 20,000 individuals are diagnosed with stomach (gastic) cancer each year. The American Cancer Society estimates that there will be 22,710 new cases of colorectal cancer diagnosed in the U.S. in 2004. Because stomach cancer may occur without symptoms, it may be in advanced stages by the time the diagnosis is made. Treatment is then directed at making the patient more comfortable and improving the quality of life.
Lung cancer causes more deaths worldwide than any other form of cancer (Goodman, G. E., Thorax 57:994-999 (2002)). In the United States, lung cancer is the primary cause of cancer death among both men and women. In 2002, the death rate from lung cancer was an estimated 134,900 deaths, exceeding the combined total for breast, prostate and colon cancer. Id. Lung cancer is also the leading cause of cancer death in all European countries, and numbers of lung cancer-related deaths are rapidly increasing in developing countries as well.
The five-year survival rate among all lung cancer patients, regardless of the stage of disease at diagnosis, is only about 13%. This contrasts with a five-year survival rate of 46% among cases detected while the disease is still localized. However, only 16% of lung cancers are discovered before the disease has spread. Early detection is difficult as clinical symptoms are often not observed until the disease has reached an advanced stage. Despite research into therapies for this and other cancers, lung cancer remains difficult to diagnose and treat effectively.
Clearly, the identification of markers and genes that are responsible for susceptibility to particular forms of solid cancer (e.g., prostate cancer, breast cancer, lung cancer, stomach cancer, colon cancer, pancreatic cancer) is one of the major challenges facing oncology today. There is a need to identify means for the early detection of individuals that have a genetic susceptibility to cancer so that more aggressive screening and intervention regimens may be instituted for the early detection and treatment of cancer. Cancer genes may also reveal key molecular pathways that may be manipulated (e.g., using small or large molecule weight drugs) and may lead to more effective treatments regardless of the cancer stage when a particular cancer is first diagnosed.
MicroRNAs are a class of small, non-coding RNAs that control gene expression by hybridizing to and triggering either translational repression or, less frequently, degradation of a messenger RNA (mRNA) target. The discovery and study of miRNAs has revealed miRNA-mediated gene regulatory mechanisms that play important roles in organismal development and various cellular processes, such as cell differentiation, cell growth and cell death (Cheng, A. M., et al., Nucleic Acids Res. 33:1290-1297 (2005)). Recent studies suggest that aberrant expression of particular miRNAs may be involved in human diseases, such as neurological disorders (Ishizuka, A., et al., Genes Dev. 16:2497-2508 (2002)) and cancer. In particular, misexpression of miR-16-1 and/or miR-15a has been found in human chronic lymphocytic leukemias (Calin, G. A., et al., Proc. Nall. Acad. Sci. U.S.A. 99:15524-15529 (2002)).
Clearly, there is a great need in the art for improved methods for detecting and treating solid cancers (e.g., prostate cancer, breast cancer, lung cancer, stomach cancer, colon cancer, pancreatic cancer). The present invention provides novel methods and compositions for the diagnosis and treatment of solid cancers.